Boron-containing jet fuel compositions



3,009,797. Patented Nov...21, 1961 ice 3,009,797 BORON-CQNTAHNDJG JET FUEL CUR [POSITIONS Fred J. Dykstra, Detroit, Mich, assignor to Ethyl Corporation, New York, N.Y., a corporation of Delaware No Drawing. Filed Apr. 9, 1956, Ser. No. 576,776 Claims. (Cl. 52-.5)

This invention relates to new compositions of matter and in particular to new jet fuel compositions characterized by high thermal stability. It also relates to new processes for improving jet fuels.

Fuel temperatures in modern jet aircraft power plants .are becoming so high that harmful deposits are formed in the precombustion phase of the fuel system. Contributing to this has been the use of the fuel as a heat sink to aid in lubricating oil cooling, which has increased fuel temperatures to the point where deposits are so severe that they interfere with normal fuel combustion as well as lubricating oil temperature control. This is so serious a problem that it can eventually lead to engine failure of the turbine section due to uneven temperature patterns. In fact, it is considered the outstanding problem in jet fuels at the present time. Attempts have been made to counteract this by redesigning and by the use of shielding materials to minimize heating of the fuel. These methods are uneconomical and also contribute substantially to the overall weight of the aircraft.

It is an object of this invention to alleviate the thermal stability problems in jet fuels. It is another object of this invention to provide new compositions of matter. A further object is to provide new jet fuel compositions which are characterized by a high degree of thermal stability. Another object is to provide a new process of treating jet fuels to impart properties of high heat stability to them.

The above and other objects of this invention are accomplished by providing a new composition of matter which comprises jet fuel which has been treated bya fuel-soluble ester of an acid of boron. Such compositions, as will be seen below, have a thermal stability of. a magnitude which is well beyond that now possessed by any other commercial fuel. In one embodiment of this invention, a jetfuel is treated with .a fuel-soluble ester of an acid of boron in such a way that the fuel after treatment contains residual amounts of said ester. Thus, in this embodiment is provided a new composition of matter which comprises jet fuel containing a minor proportion of a fuel-soluble ester of an acid of boron. In this embodiment the ester of the boron acid is preferably one which is hydrolytically stable. This type of ester is preferred because it eliminates any loss of the boron compound when the fuel comes into contact with water during processing, shipment, storage and operation.

Another preferred embodiment of this invention comprises providing as a new composition of matter a jet fuel which has been treated with a fuel-soluble meta borate ester. When jet fuel is treated with such an ester, a precipitate is formed. Upon removal of this precipitate the remaining jet fuel possesses superior characteristics. One important aspect of this mode of the invention comprises providing jet fuels which have been treated With a metaborate ester in amount such that when the resulting precipitate has been removed, the remaining fuel contains minor amounts of the metaborate ester. Another important aspect of this mode comprises providing-fuels which have been treated with a metaborate ester, and after removal of the precipitate, washed with water to remove the remaining amount of metaborate ester. Such fuels have been found to be especially susceptible to the addition of further amounts of metaborate esters or other fuel-soluble esters of boron acids. Thermal stability gains in such fuels are achieved with very-sma1l amounts of additional boron additive.

Among the hydrolytically stable esters of this invention are the glycol esters of alkyl boronic acids, the borinate esters and the boronate esters. In general, hydrolytically stable esters of a boron acid can be considered to be any which are essentially unchanged after standing in contact with its volume of water at room temperature for at least 24 hours.

The present invention also has within its purview the process-of improving jet fuel which comprises treating jet fuel with a fuel-soluble ester of an acid of boron, preferably a hydrolytically stable fuel-soluble ester of an acid of boron. Anespecially preferred embodiment of this invention comprises treating jet fuel with a fuelsoluble metaborate ester whereupon a precipitate is formed, and separating the precipitate from the treated fuel. One aspect of this mode comprises conducting this process in such a manner that residual metaborate remains in the fuel after separation of the precipitate, and another aspect of this mode comprises Washing the fuel after precipitation so that no metaborate remains. Such a fuelis especially susceptible to improvement brought about by very minor additions of further amounts of fuel-soluble esters of boron acids.

In general, the esters of this invention can be prepared from or derived from any acid of boron, including orthoboric acid (H 30 metaboric acid (H pyroboric acid (H B O sometimes referred to as mesoboric acid), the various polyboric acids, boronic acid (H BO borinic acid (H 130), etc. Suitable esters of this invention can also be prepared by esterifying the sulfur analogs of the above boron acids.

The jet fuels which comprise the majorcomponentof the new compositions of this invention are, .ingeneral, distilled liquid hydrocarbon fuels which are heavier than gasoline; i.e. they have ahigher end point than gasoline. In general, the jet fuels can be.comprised of distillate fuels and naphthas and blends of the above, including blends with lighter hydrocarbonfractions sollong as the end point of the final jet fuel'is .at least 435 .-F., and preferably greater than 480 F.

These fuels include JP3,- a mixture of about 70 percent gasoline and 30 percent light distillate having a percent evaporated point of 470 F.; JF.4, a mixture of about 75 percent gasoline and 35 percent light distillate, a fuel especially designedfor high altitude performance; -JP5, an especially fractionated kerosene; low freezing point kerosene; etc.

The following are specifications of typical liquid'hy'drocarbon jet fuels of this invention:

Fuel E Fuel F Fuel A Fuel 13 Fuel C Fuel D (J P i (kero- (JP-3) (JP-4) (JP-5) (JP-4) refsene) eree) 10% evaporated, F. 160 220 395 221 380 90% evaporated, F. 47 470 480 379 460 480 Endpoint. F 600 550 550 480 516 Gravity, API 50 i5 35 47. 3 48. 5 i3 Existent gum, mg./

ml., max 7 7 7 1.0 1. 4 1.7 Potential gum,

rug/100 ml, max 14 14 Reid vapor pressure, p.s.i 7.0 3.0 Aromatics, vol.

The following examples illustrates various specificv embodiments of this invention.

Example I To 100,000 parts of Fuel A is-added with stirring '8 parts (0.008 percent) of methyl metaborate. A flocculent precipitate is formed and this is removed by centrifugation. The resultant clear fuel which contains methyl metaborate is found to possess improved thermal stability characteristics.

Example II To 100,000 parts of Fuel B is added 5000 parts (5 percent) of n-propyl orthoborate. A fine precipitate forms and is removed by filtration. The resultant fuel which contains n-propyl orthoborate is found to possess improved thermal stability properties.

xample Ill To 100,000 parts of Fuel C is added 100 parts (0.1 percent) of diphenyl phenylboronate. The result-ant fuel blend possesses superior thermal stability characteristics.

Example IV To 100,000 parts of Fuel E is added 500 parts (0.5 percent) of dodecyl tetraborate. The resultant fuel blend is found to possess superior thermal stability characteristics.

Example V To 100,000 parts of Fuel D is added 40 parts (0.04 per cent) of methyl dibenzylborinate. The resultant jet fuel blend is found to possess thermal stability properties.

Example VI Example VIII To 100,000 parts of a liquid hydrocarbon jet fuel having an end point of 550 F. is added 100 parts (0.1 percent) of phenyl metaborate. After removal by filtration of the resulting precipitate, a clear boron-containing jet fuel of outstanding thermal property remains.

Example IX To 100,000 parts of Fuel A is added 15 parts (0.015 percent) of hexyl metaborate. The resultant precipitate is removed by filtration and the residual fuel is found to contain 5 parts of hexyl metaborate. This fuel possesses outstanding thermal stability characteristics.

Example X 100,000 parts of Fuel B are treated with 50 parts (0.05 percent) of tetramethylphenyl metaborate. After removal of the resultant precipitate the remaining metaborate ester is removed by washing with copious amounts of water at room temperature. This fuel is found to be extremely susceptible to thermal stability improvement by subsequent addition of very small amounts of fuel-soluble esters of boron acids.

Example XI To the treated, washed fuel of Example X is added with mechanical stirring 0.04 percent of the 2-methyl-2,4- pent-anediol ester of n-octyl boronic acid. The finished fuel containing this additive is found to possess superior thermal stability properties.

The substantial improvements which result from addition of these agents to jet fuel is illustrated by tests in an apparatus known as the Erdco Fuel Coker. This unit and the method of using it are described in Petroleum Processing, December 1955, pages 190911. The apparatus consists of a heated sintered steel filter through which a preheated fuel is passed at a regulated rate. The time which it takes for the pressure drop across the filter to reach 25 inches of mercury is taken as a measurement of the coking tendencies of the fuel and, therefore, as a measurement of the fuels thermal stability characteristics. A fuel that runs through the apparatus for a full 300 minutes without causing any pressure drop is considered thermally stable. The ideal fuel would pass through the filter indefinitely without causing any pressure drop.

In a test in the Erdco coking apparatus a sample of Fuel D which had not been treated according to the terms of this invention was passed through the filter until the pressure drop across the filter reached 25 inches of mercury. The fuel was preheated to 325 F. and the filter was maintained at a temperature of 500 F. The pressure on the fuel was 150 pounds per square inch. The time required for the pressure drop across the filter to reach 25 inches of mercury was only minutes. In contrast when the same fuel was passed through the same apparatus under the same conditions except that it had been treated with 0.015 percent of butyl metaborate, and the resulting precipitate removed by filtration, the pressure drop across the filter after a running time of 300 minutes was only 8.75 inches of mercury.

In another test, Fuel E which had not been treated according to the terms of this invention was run through the apparatus under the same conditions. It took only 47 minutes for the pressure drop across the filter to reach 25 inches of mercury. On the other hand, when this run was repeated with Fuel E, treated with 0.023 percent of butyl metaborate, it took 198 minutes to reach this pressure drop. With 0.045 percent of butyl metaborate a pressure drop of 25 inches of mercury was reached in 196 minutes.

Similar results are obtained with other boron esters of this invention in the above and other jet fuels. For example, when Fuel E was tested in the Erdco coking apparatus under the same conditions as the above runs but containing 2.04 percent of isopropyl orthoborate the apparatus ran for the full 300 minutes without any pressure drop whatsoever across the filter.

It will be noted that the amounts of metaborate additives which cause substantial improvements in the thermal stability characteristics of jet fuels are exceedingly small. This is an outstanding property of the metaborate, and this is one reason that they are preferred compounds of this invention. Another reason that the metaborates and certain other boron compounds are preferred is that they have the property of apparently reacting with certain impurities in the jet fuel to cause their removal by precipitation. It is not certain just what these impurities are although it is now known that the metaborates and certain other of the boron compounds of this invention react with nitrogen compounds, peroxides and water to form precipitates. Although I am not bound by this theory, it appears that there may be some connection between the formation of such precipitates and the extreme effectiveness of the metaborates.

The types of boron compounds which this invention uses have been briefly described above. The most important classes are alkyl orthoborates, aryl orthoborates, cycloalkyl orthoborates, alkyl metaborates, aryl metaborates, cyeloalkyl metaborates, alkyl pyroborates, aryl pyroborates, cycloalkyl pyroborates, alkyl polyborates, aryl polyborates, cycloalkyl polyborates, dialkyl alkylbor- .onates, diaryl alkylboronates, dicycloalkyl alkylboronates,

dialkyl arylboronates, diaryl arylboronates dicycloalkyl arylboronates, dialkyl cycloalkylboronates, diaryl cycloalkylboronates, dicycloalkyl cycloalkylboronates, diol and polyol esters of alkyl, aryl and cycloalkyl boronates, alkyl dialkylborinates, aryl dialkylborinates, cycloalkyl dialkylborinates, alkyl diarylborinates, aryl diarylborinates, cyclo- -alkyl diarylborinates, alkyl dicycloalkylborinates, aryl dicycloalkylborinates and cycloalkyl dicyoloalkylborinates.

The organic portion of the molecule can consist of an alkyl, aryl or cycloa-lkyl radical, and a given ester can be composed entirely of one type of such radicals. The alkyl radicals can be methyl, ethyl, propyl, butyl, amyl, etc. up to at least C alkyl radical, but for reasons of economy alkyl radicals of 1 to 12- carbon atoms are pre ferred. Typical alkyl esters of this invention include methyl orthoborate, butyl orthoborate, isobutyl orthoborate, decyl orthoborate, methyl metaborate, ethyl metaborate. isopropyl metaborate, hexyl metaborate, dodecyl tetraborate, cetyl metaborate, tetraphenyl tetraborate, tetrapropyl pyroborate, methyl dimethylborinate, octyl di-secbutylborinate, methylethyl methylboronate, didecyl butylboronate, and the like. Cycloalkyl compounds include cyclohexyl orthoborate, cyclohexyl thiomet-aborate, dicyclohexyl cyclohexylborinate, cyclohexyl tetraborate, tetracyclopentyl pyroborate, etc. C and C cycloalkyl radicals are preferred. Typical aryl derivatives include triphenyl orthoborate, phenyl metaborate, benzyl metaborate, tetratolyl pyroborate, phenyl dibenzylborinate, di-(phenyl)- phenylboronate, and the like. Aromatic hydrocarbon radicals of 6 to 10 carbon atoms are preferred.

Mixed alkyl, aryl and cycloalkyl compounds also come within the scope of this invention. Thus, for example, can be provided diphenylmethyl orthoborate, toly-ltributyl pyroborate, dimethyl phenylboronate, and the like. The sulfur analogs of the above are also useful.

A variety of methods are avail-able for preparing the boron compounds of this invention. The orthoborates may be conveniently prepared by esterifying orthoboric acid with the appropriate alcohol or phenol or mixture of the two. Temperatures of around 80 C. are quite satisfactory. The metaborates can be prepared by reacting the appropriate alcohol or phenol with orthoboric acid in proper molar ratio in the presence of a diluent which removes water azeotropically, e.g., toluene. Boronate esters can be prepared by reacting boron t-rihalide with Grignard reagent to form the acid dihalide of boronic acid and then reacting the dihalide with the appropriate alcohol or phenol. Preparation of borinate esters is analogous. Other methods for preparing the various esters of this invention will occur to those skilled in the art.

The amount of fuel-soluble ester of an acid of boron that is used to treat the jet fuel of this invention can range from about 0.008 percent to about 5 percent by weight. Ordinarily, amounts of 0.04 to 0.2 percent are found to be quite effective. In the case of the outstanding metabor-ates of this invention, good results are obtained at concentrations ranging from 0.008 percent to about 0.1 percent. In the embodiment which comprises treating jet fuel with a metaborate ester and then adding a fuel-soluble ester of an acid of boron to the treated fuel as an additive, the amount of said additive will usually range from 0.02 percent to 0.5 percent for best results. When the hydrolytically stable esters are employed as additives, small amounts are used because, due to their hydrolytic stability these esters remain unchanged in the fuel for indefinite periods.

Although good results are usually obtained by conducting the treatment of jet fuels at temperatures in the neighborhood of room temperature, .it is entirely feasible to operate at temperatures ranging from 0 C. to 160 C., preferably not greater than C.

I claim:

1. As a new composition of matter, jet fuel consisting essentially of distilled liquid hydrocarbon fuel heavier than gasoline, the end point being at least 480 F., containing a minor amount, namely, 0.008% to 5% by weight, of a fuel-soluble ester of an acid of boron, said acid being selected from the class consisting of orthoboric acid, metaboric acid, py-roboric acid, boronic acid and borinic acid, the esterifying groups in said ester being selected from the class consisting of alkyl radicals of l to 12 carbon atoms, cyoloalkyl radicals of 5 to 6 carbon atoms, aryl radicals of 6 to 10 carbon atoms and mixtures thereof.

2. The composition of claim 1 in which the fuel-soluble ester is di-(catechol)pyroborate.

3. Process of improving jet fuel which comprises treating said fuel with a fuel-soluble ester of metaboric acid, the esterifying groups in said ester being selected from the class consisting of alkyl radicals of 1 to 12 carbon atoms, cycloalkyl radicals of 5 to 6 carbon atoms, aryl radicals of 6 to 10 carbon atoms and mixtures thereof, sep arating said fuel from the precipitate which is formed and adding to said separated fuel from 0.02 to 0.05 percent by weight of an ester of an acid of boron, said acid being selected from the group consisting of orthoboric acid, metaboric acid, pyroboric acid, boronic acid and borinic acid, the esterifying groups in said ester being selected from the group consisting of alkyl radicals of 1 to 12 carbon atoms, cycloalkyl radicals of 5 to 6 carbon atoms, aryl radicals of 6 to 10 carbon atoms and mixtures thereof.

4. A process for cooling the lubricating oil in a jet engine comprising using as a coolant for heat transfer with said lubricating oil a thermally stabilized jet fuel consisting essentially of distilled liquid hydrocarbon fuel having an end point of at least 480 F., said end point being higher than that of gasoline, said fuel containing from about 0.008 to about 5 percent by weight of a fuel soluble ester of an acid of boron, said acid being selected from the class consisting of orthoboric acid, metaboric acid, pyroboric acid, boronic acid and borinic acid, the esterifying groups in said ester being selected from the class consisting of alkyl radicals of 1 to 12 carbon atoms, cycloalkyl radicals of 5 to 6 carbon atoms, aryl radicals of 6 to 10 carbon atoms and mixtures thereof.

5. Process of improving jet fuel consisting essentially of distilled liquid hydrocarbon fuel heavier than gasoline, the end point being at least 480 R, which comprises adding to said fuel a fuel-soluble ester of metaboric acid, the esterifying groups of said ester being selected from the class consisting of alkyl radicals of 1 to 12 carbon atoms, cyoloalkyl radicals of 5 to 6 carbon atoms, aryl radicals of 6 to 10 carbon atoms and mixtures thereof, and separating said fuel from the precipitate which is formed.

Darling et a1. June 7, 1955 Pay et al Oct. 16, 1956 

1. AS A NEW COMPOSITION OF MATTER, JET FUEL CONSISTING ESSENTIALLY OF DISTILLED LIQUID HYDROCARBON FUEL HEAVIER THAN GASOLINE, THE END POINT BEING AT LEAST 480*F., CONTAINING A MINOR AMOUNT, NAMELY, 0.008% TO 5% BY WIEGHT, OF A FUEL-SOLUBLE ESTER OF AN ACID OF BORON, SAID ACID BEING SELECTED FROM THE CLASS CONSISTING OF ORTHOBORIC ACID, METABORIC ACID, PYROBORIC ACID, BORONIC ACID AND BORINIC ACID, THE ESTERIFYING GROUPS IN SAID ESTER BEING SELECTED FROM THE CLASS CONSISTING OF ALKYL RADICALS OF 1 TO 12 CARBON ATOMS, CYCLOALKYL RADICALS OF 5 TO 6 CARBON ATOMS, ARYL RADICALS OF 6 TO 10 CARBON ATOMS AND MIXTURES THEREOF. 